The present invention discloses a method for a network to choose an
authentication mode, wherein the key lies in that, according to the received
authentication information in the
authentication vector request message from S-CSCF as well as according to type of the requesting subscriber, HSS returns
authentication information of the Early-IMS-based authentication vector to S-CSCF, or returns
authentication information of the Full-IMS-based authentication mode to S-CSCF, or directly returns failure information to S-CSCF. If it is under the former two situations, the subscriber will be authenticated by adopting the corresponding authentication mode, and then S-CSCF will return access-allowed or access-rejected information to the subscriber according to authentication result. If it is in the latter situation, S-CSCF will directly send access-rejected information to the subscriber. By applying the present invention, the network can choose a proper authentication mode to authenticate the subscriber according to the subscriber's requirements, so that
processing ability of the network is enhanced and the network is compatible with original security protocols to the fullest extent.